1. Field of the Invention
This invention relates to optical systems with means for stabilizing the movement of an image that occurs against unexpected shakes.
2. Description of the Related Art
When pictures are being taken from on a moving vehicle such as a running car or a flying aircraft, vibrations propagate to the photographic system so that the blurring will appear in the taken photographs.
Methods of preventing the image from blurring in taking pictures, or image stabilizing optical systems have been proposed in, for example, Japanese Laid-Open Patent Applications Nos. Sho 50-80147 and 61-223819 and Japanese Patent Publication No. Sho 56-21133.
Japanese Laid-Open Patent Application No. Sho 50-80147 discloses a zoom lens having two afocal systems for varying the image magnification, wherein letting the angular magnification of the first system be denoted by M.sub.1 and the angular magnification of the second system by M.sub.2, the relationship: M.sub.1 =1-1/M.sub.2 is maintained when the image magnification is varied, while the second system is held in fixed spatial alignment with the original line of sight to compensate for the movement of the image. Thus, the image is stabilized.
Japanese Patent Publication No. Sho 56-21133 employs means for detecting the vibratory state of the optical instrument, whereby the direction in which either the lens unit behind the zoom section, or an optical member such as mirror is to move is controlled in accordance with its output signal so that the accidental displacement of the image due to the shake is canceled, thus achieving stabilization of the image.
Japanese Laid-Open Patent Application No. Sho 61-223819 provides for the photographic system with a refraction type variable vertex-angle prism in the frontmost position, wherein variation of the vertex angle of the prism is controlled in accordance with displacement of the photographic system to deflect the image, thus achieving stabilization of the image.
Besides these, Japanese Patent Publications Nos. 56-34847 and 57-7414 disclose photographic systems of which one constituent optical member is arranged to be held in fixed spatial alignment with the line of sight against shakes, wherein upon angular deviation of the housing of the system, this optical member generates a prism. By utilizing this effect, the image of an object in the line of sight is deflected to such a direction that it remains stationary at the focal plane. Also, U.S. Pat. No. 2,959,088 discloses an image stabilizing optical system for the device concerning telescopes. Further there is U.S. Pat. No. 3,378,326.
It is also known to utilize the acceleration sensor in detecting occurrence of shakes of the photographic system. Responsive to a signal obtained at this time, a lens group constituting part of the photographic system is made to vibrate in a plane perpendicular to the optical axis so that a stationary image is obtained at the focal plane. As this example there are U.S. patent applications Ser. Nos. 261,231 filed on Oct. 24, 1988; 156,930 field on Feb. 17, 1988; 116,541 filed on Nov. 4, 1987; and 116,668 filed on Nov. 4, 1987.
By the way, for the case of adding the capability of image stabilization to the zoom lens system, a necessity usually arises that, depending on the varied focal length of the entire system, an additional compensation be made to the image stabilizing optical member, as, for example, Japanese Patent Publication No. 56-21133 suggests. Also, as Japanese Laid-Open Patent Application No. Sho 50-86147 suggests, some limitations must be set forth.
In general, to facilitate a minimization of the stress in the operating mechanism for decentering one lens group of the photographic system to compensate for the image movement to obtain the stationary image at the focal plane, the photographic system is required to be of the form that the relationship between the amount of deflection of the image and the amount of decentering movement of that lens group is simplified.